basic electronics question

You cannot accurately measure .X anything resistance. I'm sure that it DOES measure "a short." The purpose of a resistor like that is often for metering (operating drop across the resistor goes to a meter, like an external shunt ammeter), or for protection/ stabilization similar to a ballast, or to act like an emergency fuse.

In fact, setting up a current drawing situation is exactly one way to measure very low resistances........accurately measure the voltage drop with a known accurate current flowing.

I don't know anything about these amps, be aware the diagram could be drawn incorrectly as well

Also one way to test it at low power output settings and somewhat protect the circuit from further damage, is to connect the power supply with a series light bulb. A "real" light bulb. You'l have to experiment with wattage, I'd say at least 100 and maybe 200. If you can drum up some cheap sockets, you can parallel bulbs to get the wattage.